What is Allicin? - Definition, Chemical Formula & Properties

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

In this lesson, our primary focal point will be on an organosulfur compound called allicin. Our main topics of discussion will include its definition and structure, chemical formula, and properties the compound exhibits.

The Smell of Fresh Garlic

Do you like to cook at home? One of the most popular produce items to cook with in a lot of cuisines around the world is garlic. Garlic cloves are utilized in Italian dishes, recipes that originate in India, and a lot of popular American dishes as well. When you're slicing or mincing garlic cloves there's always this strong (and, depending on your preference, pleasant) characteristic odor produced.

Have you ever wondered what was actually responsible for that smell? As it turns out, the organic chemistry the garlic plant carries out can take credit for that. We're going to be learning about the specific compound that the garlic plant produces that's attributed to its unique odor. This compound is called allicin, and we'll be taking a detailed look at its definition, its structure, its chemical formula, and a couple of its more important properties. Let's slice some garlic!

Definition of Allicin

Let's get our discussion started by looking at the definition of the compound. Allicin is an organosulfur compound that's produced by garlic plants, and was discovered/isolated by the chemists Chester J. Cavallito and John Hays Bailey in 1944. It's called an organosulfur compound because it's organic in nature (primarily composed of carbon and hydrogen atoms) and it contains the element sulfur as well. As we'll see when we talk about the structure, the molecule actually contains two sulfur atoms in total.

What's interesting about allicin, is you won't find it in an intact garlic clove. Unless that garlic gets chopped or sliced, no allicin is made. Chopping or slicing the garlic activates an enzyme called alliinase, which helps produce allicin. We'll explore this further when we talk about the properties of allicin!

Chemical Formula and Structure of Allicin

We've already mentioned that allicin is an organosulfur compound and that it only contains carbon, hydrogen, and sulfur, but how many of each of those atoms does it contain? It turns out that allicin contains six carbon atoms, ten hydrogen atoms, one oxygen atom, and two sulfur atoms. This makes the chemical formula C6 H10 OS2.

From a structural standpoint, allicin contains several important distinguishing features. First notice how it contains two alkene functional groups, one at each end of the molecule. An alkene functional group is one that contains a carbon-carbon double bond. The structure also contains a sulfur-oxygen bond with the sulfur atom possessing a formal positive charge and the oxygen bearing a formal negative charge.

The structure of allicin

Notice in the structure that the compound contains a sulfur-sulfur bond, which is called a disulfide bond. This is sometimes referred to as a disulfide linkage. This feature of the molecule will come into play when we discuss the properties of allicin.

Properties of Allicin

Before we wrap up let's talk about a couple important properties of allicin. Probably one of the most important chemical properties of the compound is the disulfide linkage we just mentioned. When garlic cloves are chopped, cut, or crushed, there's an enzyme called alliinase in the garlic that starts to produce allicin. The allicin that's made is unstable because of the weak sulfur-sulfur bond, and it quickly decomposes to form other sulfur-containing compounds that give garlic its characteristic smell and taste.

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